1. Field of the Invention
The present invention relates to a turbomolecular pump, and more particularly to a turbomolecular pump having improved stator blades.
2. Description of the Related Art
A turbomolecular pump is widely used as a vacuum apparatus for a semiconductor manufacturing equipment.
The turbomolecular pump has stator blades and rotor blades which are disposed on a stator portion and a rotor portion, respectively, in a multistage arrangement in an axial direction, and the rotor portion is rotated with a motor at high speed so that a vacuum (exhaust) action is performed.
FIGS. 11(a) to 11(c) show the structures of the rotor blade and the stator blade of the turbomolecular pump described above. FIG. 11(a) shows an arrangement between the rotor blade and the stator blade, FIG. 11(b) is a sectional perspective view showing a rotor that is cut along upper and lower planes of the rotor blade, and FIG. 11(c) is a perspective view showing a part of the stator blade.
As shown in FIG. 11(a), the turbomolecular pump is composed of a rotor 60 and a stator 70 that are fixedly disposed to rotor axes rotating at high speed.
The rotor 60 is composed of a rotor body 61 that accommodates a motor and magnetic bearings inside thereof, a rotor ring portion 64 arranged at an outer circumference of the rotor body 61, and a plurality of blades 63 provided to the rotor ring portion 64 radially in a radial direction and tilted at a predetermined angle with respect to the rotational axis.
On the other hand, the stator 70 is composed of a spacer 71 and a stator blade 72 that are arranged between rotor blades 62 at the respective stages, while being supported its outer circumferential side between the spacers 71 and 71.
The spacer 71 is a cylindrical shape having stepped portions, and the length of each stepped portion in an axial direction, located inside thereof, is varied in accordance with the intervals between the respective stages of the rotor blades 62.
The stator blade 72 is composed of an outer ring portion 73, part of outer circumferential portion of which is sandwiched by the spacers 71 in circumference direction, an inner ring portion 74, and a plurality of blades 75 both ends of which are supported radially with a predetermined angle by the outer ring portion 73 and the inner ring portion 74. The inner diameter of the inner ring portion 74 is formed to have a larger size than the outer diameter of the rotor body 61 so that an inner circumferential surface 77 of the inner ring portion 74 and an outer circumferential surface 65 of the rotor body 61 do not contact with each other.
In order to arrange the stator blade 72 between the rotor blades 62 at the respective stages, each stator blade 72 is divided into two parts in circumference. The stator blade 72 is made from a thin plate such as a stainless or aluminum thin plate that is divided into two. An outer portion having a semi-ring profile and portions for blades 75 of the stator blade 72 are cut out by means of etching from the thin plate, and the portions for blades 75 are folded by means of press machining to have a predetermined angle. Thus, the shape shown in FIG. 11(c) is obtained.
In the thus formed turbomolecular pump, the rotor 60 is designed to be rotated with a motor at several tens of thousands r.p.m., so that an exhaust action is effected from the upstream side to the downstream side of FIG. 11(a)
In such conventional turbomolecular pump, since the support of the stator blades 72 by a spacer 71 is carried out with a cantilever configuration and the stator blades 72 are divided into two parts in circumference, large deflection would occur in the case that excess loads were applied to the stator blades 72. In particular, in the stator blades 72 formed by means of press machining, since the thickness of the plate is thin, there have been cases where the open end on the center side was largely deflected at the portion divided into two parts.
For that reason, in the case where a large fluctuation occurred in a load of gas due to malfunction, etc. of valves attached to a vacuum chamber, the stator blades were caused to largely deflect with the result that, in the worst case, blades 75 of the stator blades were brought into contact with blades 63 of the rotor blades were damaged.
Further, in the case where such a structure was employed that a magnetic bearing was used for the rotor axis, there also occurred the case in which the stator blades 72 and the rotor blades 62 broken when brought into contact with each other due to vibration generated at the time of a trouble with the magnetic bearing device or of a touch-down of a touch down bearing upon a power failure.
The present invention has been made to solve the above-mentioned problems inherent in the conventional turbomolecular pump, and therefore has a primary object of the present invention to provide a turbomolecular pump with stator blades having a structure in which deflections are not relatively occurred.
Further, a secondary object of the present invention is to provide a turbomolecular pump with stator blades having a structure in which deflections are not relatively occurred.
Further, a secondary object of the present invention is to provide a turbomolecular pump with stator blades having a structure in which breakage of the stator blades are hardly occurred even if the stator blades are brought into contact with rotor blades due to deflections.
In order to attain the primary object of the present invention, according to the present invention, a reinforcement portion is arranged to the inner ring portion of each stator blade.
Further, according to the present invention, the reinforcement portion is constructed of a rib structure formed in the inner ring portion of the stator blade.
Still further, according to the present invention, said reinforcement portion is constructed of engagement means formed at end portions of the divided inner ring portion of the stator blade for engaging one end portion of the divided inner ring portion of said stator blade and the other end portion of the divided inner ring portion facing thereto.
In order to attain the secondary object of the present invention, according to the present invention, the blades of the stator blades at the respective stages comprise a multi-layer of plural pairs of blades overlapped with each other, and the phases of the divided positions at the respective layers are shifted with each other.
Further, according to the present invention, the blades of the rotor blades at the respective stages are provided to the rotor ring portion that is disposed to the rotor corresponding with the stage; and an outer diameter of the inner ring portion of the blades of the stator blades is smaller than an outer diameter of the rotor ring portion.
Further, according to the present invention, steps are formed at the outer ring portion so that the blades of the stator blades are allowed to contact with the outer ring portion.